This research work focuses on the role of prostaglandin synthesis in blood coagulation. Specifically, the work involves purification and characterization of two enzymes of prostaglandin synthesis: prostaglandin synthetase and prostaglandin H yields E isomerase. Prostaglandin synthetase is the first enzyme in the biosynthetic pathway, catalysing the formation of PGH from the substrate arachidonic acid. Prostaglandin H yields E isomerase catalyses the formation of PGE from PGH. Recent results indicate that aspirin (acetyl salicylic acid) acetylates PG synthetase at a single serine residue (J. Biol Chem. 253:3782, 1978) and inhibits enzyme activity by this mechanism. Further work has been directed at determining the NH2 terminal sequence of the protein in both acetylated and non-acetylated form. In addition to structural studies, a radio-immune assay for PG synthetase has been developed which can detect nanogram amounts of the protein. Lastly, work has been started on determining which pharmacologic agents inhibit PG H yields E isomerase.